title: Aryl nitrene rearrangements: spectroscopic observation of a benzazirine and its ring expansion to a ketenimine by heavy-atom tunneling.
abstract: In the photodecompositions of 4-methoxyphenyl azide (1) and 4-methylthiophenyl azide (5) in argon matrixes at cryogenic temperatures, benzazirine intermediates were identified on the basis of IR spectra. As expected, the benzazirines photochemically rearranged to the corresponding ketenimines and triplet nitrenes. Interestingly, with the methylthio substituent, the rearrangement of benzazirine 8 to ketenimine 7 occurred at 1.49 × 10(-5) s(-1) even in the dark at 10 K, despite a computed activation barrier of 3.4 kcal mol(-1). Because this rate is 10(57) times higher than that calculated for passing over the barrier and because it shows no temperature dependence, the rearrangement mechanism is interpreted in terms of heavy-atom tunneling.
authors.affiliation: Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan. h-inui@kitasato-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Inui
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Sawada
authors.forename: Shigero
authors.initials: S
authors.lastname: Oishi
authors.forename: Kiminori
authors.initials: K
authors.lastname: Ushida
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McMahon
mesh_terms: D001388:Aziridines / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared
chemical_list: D001388:Aziridines; D007659:Ketones